It is well known that turfs for sport fields such as for soccer, hockey, cricket, rugby, etc. provide a natural turf grown on a ground or substrate. Natural turfs offer high aesthetical, technical and environmental performances.
However, with the use and with time, as well as with unfavorable weather conditions the natural turf quickly wears and requires expensive maintenance work. Unless a worn natural turf is completely restored the field there is anaesthetical, irregular, and potentially dangerous for the users.
An intense activity, which normally concerns a sport field, worsens the turf characteristics after each use without enough time for the turf to recover. In particular, the field looses its planarity, uniformity and resistance of its substrates, affecting the athletic performances and endangering the athletes.
For these reasons, fields of artificial blades have been developed in the last years, having artificial grass blades and granular filling material, for example sand or resilient material, which presents better performances and steadiness of grip on the ground. Such artificial turfs can be installed on surfaces made of various material, in particular asphalt, and stabilized inert material.
Artificial turfs have some technical drawbacks, among which a considerable superheating of the field in addition to environmental modifications with subsequent discomfort for the users. For avoiding the above described drawbacks combined systems have been proposed of mixed natural and artificial turf. A combined system natural/artificial is described in U.S. Pat. No. 6,145,248. It provides substantially a biodegradable substrate to which grass blades are connected of artificial material and on which a layer is located of soil in which is natural grass is sowed. With time the roots of the grass spread and the biodegradable substrate disintegrates. Therefore, the roots reach the ground located underneath the substrate and radicate in it.
However, this solution is strictly bound to the availability of a ground and has strong applicative limits, because it cannot be used in case of surfaces where artificial turfs are usually installed.